1. Field of the Invention
The present invention relates generally to a multifunctional visceral catheter which is substantially self-guiding, i.e., which may be positioned in a visceral venous system without the need for bedside fluoroscopy or other x-ray devices.
More particularly, the self-guiding system of the catheter according to the invention comprises sensor systems which are sensitive to an analyte or metabolite having a substantial extraction fraction across the splanchnic bed or vascular circuit being explored. When the catheter is properly positioned, such as in the hepatic or renal vein, the first sensor system will yield signals reflecting a substantially higher concentration of the given analyte or metabolite than will a second sensor system positioned in the hepatic or renal venous system, thus readily confirming proper positioning of the catheter.
The catheter according to the invention is also capable of performing various monitoring and assessment functions. The catheter is capable of continuously monitoring the oxygen saturation in the hepatic or renal venous blood once the catheter is placed in any major hepatic or renal venous vessel. The catheter according to the invention also has the capability of measuring absolute hepatic or renal blood flow using a tracer clearance technique. Further, the catheter permits direct sampling of venous blood, such as hepatic or renal venous blood, for the ex vivo measurement of metabolite concentrations.
2. Description of Relevant Art
Known methods of diagnosing liver and/or kidney dysfunction, as well as assessing various physiological parameters associated with the functioning of these organs, typically require catheterization of the hepatic or renal venous systems. A principal disadvantage associated with known techniques for catheterizing the hepatic and renal venous systems is that bedside fluoroscopy or other x-ray devices are required in order to properly position the catheter. For example, while a thermodilution catheter has been developed for renal blood flow determination which might be applicable to general clinical use, the need for fluoroscopic assistance in positioning such catheter is a critical shortcoming. See M. Brenner, G. L. Schaer, D. L. Mallory, et al, "Detection of renal blood flow abnormalities in septic and critically ill patients using a newly designed indwelling thermodilution renal vein catheter", Chest, Vol. 98, pp. 170-79 (1990).
The present invention overcomes this major shortcoming of known catheterization techniques by providing a visceral catheter which is effectively self-guiding, i.e., which permits positioning of the catheter in either the hepatic or the renal venous systems without the use of bedside fluoroscopy or other x-ray devices.
In addition to this novel self-guiding feature, the multifunctional visceral catheter according to the invention also permits continuous monitoring of the oxygen saturation in the hepatic or renal venous blood. Heretofore, there has been no known technique for readily assessing individual organ oxygenation. Instead, central mixed venous oxygen saturation has commonly been used as an index of global body oxygenation, without any assessment of individual organ function or oxygenation. However, the results of various studies have shown that a :marked reduction in hepatic venous oxygen saturation frequently exists in critically ill patients. See, e.g., Michael S. Dahn, M. Patricia Lange, Robert F. Wilson, Lloyd A. Jacobs, and Robert A. Mitchell, "Hepatic blood flow and splanchnic oxygen consumption measurements in clinical sepsis," Surgery, Vol. 107, No. 3, pp. 295-301 (March 1990). This condition goes undetected when only global body oxygenation is assessed, leaving the physician unaware of a condition which could otherwise be therapeutically addressed through the use of cardioactive drugs or blood transfusion. To overcome this problem, the multifunctional visceral catheter according to the present invention is capable of continuously monitoring regional oxygenation. Thus, once the catheter according to the invention is placed in a major hepatic vessel, hepatic function can be assessed in a more direct fashion than is possible by conventional means, such as by monitoring serum bilirubin or liver enzymes.
Similarly, the novel catheter according to the invention permits convenient, direct monitoring of the renal venous system. By positioning the catheter according to the invention in the renal vein, endogenous creatinine clearance and other renal functional indicators can be critically assessed. Further, if inulin and/or para-aminohypurate are available for intravenous infusion, glomerular filtration rate and renal blood flow can be assessed.